1. Field of the Invention
The present invention relates to an EGR flow rate control apparatus of an internal combustion engine for measuring an EGR gas flow rate in an EGR flow channel and controlling an EGR gas flow rate, and more particularly to an EGR flow rate control apparatus of an internal combustion engine that is suitable for reducing NOx and PM (soot) in exhaust gases of an internal combustion engine.
2. Background Art
In recent years, among various kinds of engines, a hopeful view is being taken of diesel engines and ignition lean-burn engines with regard to enhancing the fuel consumption of internal combustion engines. However, compared to other engines, the exhaust gases of diesel engines and lean-burn engines tend to include a large amount of NOx (nitrogen oxides). Diesel engines also discharge PM (soot) in addition to NOx. In such engines, in order to decrease the amount of NOx or PM included in the exhaust gases it is effective to lower the fuel combustion temperature, and exhaust gas recirculation (EGR) control is conventionally performed that carries out combustion control that returns a portion of the exhaust gas to the intake side via an EGR flow channel that communicates an exhaust pipe with an intake pipe.
For this purpose, an EGR flow rate control apparatus has been proposed as disclosed, for example, in JP Patent Publication (Kokai) No. 2006-214275A, in which a sensor (EGR flow sensor) that measures an EGR gas flow rate is disposed in an EGR passage and the control apparatus controls a lift amount (degree of opening) of the EGR control valve (EGR valve) so that a measured value obtained by the EGR flow sensor becomes a target value that is calculated by the control apparatus.